Gale Warning 465, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKDT SAT AUG 10 2013

.ANALYSIS AND UPPER LEVELS...
A LONGWAVE TROUGH REMAINS CENTERED OVER THE EASTERN BERING SEA WITH A
PARENT LOW PRESSURE SYSTEM OFF THE COAST NEAR BETHEL. SIGNIFICANT
SHORTWAVES CONTINUE TO ROUND THE BASE OF THE LONGWAVE TROUGH AND MOVE
NORTHWARD INTO SOUTHERN ALASKA...BRINGING PERIODS OF WIDESPREAD
MODERATE RAIN. THE MOST RECENT SHORTWAVE THAT BROUGHT RAIN THIS
MORNING TO THE AREA IS DEPARTING TO THE NORTH...WITH THE BACK EDGE OF
THE RAIN NOW OVER THE COPPER RIVER BASIN AND SUSITNA VALLEY AREAS.
RAINFALL AND HIGH FREEZING LEVELS HAVE ALLOWED RIVERS AND STREAMS
AROUND VALDEZ TO RISE TO NEAR BANKFULL...AND A FLOOD ADVISORY IS IN
EFFECT THROUGH THIS EVENING AS RAINFALL IS EXPECTED TO RELENT LATE
THIS AFTERNOON. MEANWHILE...SOME BREAKS IN THE CLOUDS ARE DEVELOPING
BEHIND THIS FEATURE OVER THE KENAI PENINSULA. PRECIPITATION IS MORE
SHOWERY OVER THE SOUTHWEST MAINLAND AND EASTERN BERING
SEA...ASSOCIATED PRIMARILY WITH THE LOW CENTER SPINNING NEAR NUNIVAK
ISLAND. THE WESTERN HALF OF THE BERING SEA AND ALEUTIANS ARE UNDER
THE INFLUENCE OF HIGH PRESSURE...WITH FAIRLY TRANQUIL BUT CLOUDY
WEATHER OCCURRING AT MOST SPOTS.

.MODEL DISCUSSION...
MODELS ARE IN GOOD OVERALL AGREEMENT...BUT DISAGREE ON SOME OF THE
KEY DETAILS OF THE FORECAST EVEN IN THE NEXT 24 HOURS. WHAT THE
MODELS DO HAVE IN COMMON IS THAT YET ANOTHER WAVE WILL MOVE NORTHWARD
THROUGH THE TROUGH ON SUNDAY AND BRING ANOTHER ROUND OF SIGNIFICANT
RAINFALL TO THE SOUTHERN MAINLAND. THE INTENSITY AND PLACEMENT OF
THIS FEATURE IS MORE PROBLEMATIC...WITH THE GFS/EC NOW SINGING FROM
THE SAME SHEET OF MUSIC AND BRINGING A MORE SIGNIFICANT ROUND OF RAIN
IN TO PRINCE WILLIAM SOUND AND ANCHORAGE TOMORROW...WITH THE BACK
EDGE POSSIBLY REACHING WESTWARD TO INCLUDE THE WESTERN KENAI
PENINSULA. PREVIOUS RUNS OF THE NAM HAD KEPT THE COOK INLET AREA MUCH
DRIER...BUT ARE NOW TRENDING STRONGER AND WETTER WITH THIS FEATURE
SIMILAR TO THE GFS/EC. FURTHER OUT...THE OTHER SIGNIFICANT MODEL
DISCREPANCY OCCURS DURING THE DAY TUESDAY. MODELS YESTERDAY WERE
GENERALLY SHOWING WEAK HIGH PRESSURE BUILDING INTO SOUTHERN ALASKA ON
TUESDAY...BUT THE OVERNIGHT RUNS AS WELL AS THE 18Z NAM HAVE BEGUN A
TREND TOWARD A MIDLEVEL TROUGH REMAINING SOMEWHERE AROUND COOK
INLET...KEEPING MORE CLOUDS AND LINGERING RAIN AND SHOWERS AROUND.
THE AFTERNOON FORECAST WILL TREND TOWARD A WETTER SOLUTION FOR BOTH
OF THE AFOREMENTIONED FEATURES...UTILIZING PRIMARILY A
CONSENSUS-BASED APPROACH AMONG THE MODELS.

.SHORT TERM FORECAST...

SOUTHCENTRAL...RAIN HAS ENDING FROM ANCHORAGE SOUTHWARD EARLY THIS
AFTERNOON...AND SOME BREAKS OF SUN ARE POSSIBLE AROUND COOK INLET
THIS AFTERNOON. SOME PATCHY FOG IS POSSIBLE OVER THE WESTERN KENAI
OVERNIGHT IF PARTIAL CLEARING PERSISTS THROUGH MUCH OF THE NIGHT.
MEANWHILE...SATELLITE IMAGERY INDICATES THE NEXT BATCH OF RAIN IS
ALREADY TAKING SHAPE IN THE SOUTHERN GULF AS MOISTURE STREAMS QUICKLY
BACK TOWARD THE MAINLAND. CONFIDENCE IS INCREASING THAT THE ANCHORAGE
BOWL AND PRINCE WILLIAM SOUND REGION WILL AGAIN SEE SIGNIFICANT
RAINFALL ON SUNDAY. WIDESPREAD RAIN WILL THEN TAPER TO MORE SHOWERY
CONDITIONS ACROSS MOST OF THE AREA THAT NOW LOOK TO PERSIST THROUGH
EARLY WEDNESDAY MORNING.

SOUTHWEST MAINLAND...WIDESPREAD SHOWERS WILL CONTINUE THROUGH
TOMORROW...ENHANCED BY LIMITED AFTERNOON/EVENING SOLAR HEATING. SOME
ISOLATED THUNDERSTORMS ARE POSSIBLE AGAIN TODAY OVER THE LOWER
KUSKOKWIM VALLEY...AND MAY EVEN SPREAD BACK INTO INTERIOR PORTIONS OF
THE DELTA IF ENOUGH CLEARING DEVELOPS THIS AFTERNOON. WEAK SOUTHERLY
FLOW WILL CONTINUE THROUGH THE SHORT TERM FORECAST PERIOD...LEAVING
COASTAL SITES VULNERABLE TO CLOUDS AND FOG MOVING ONSHORE.

BERING SEA/ALEUTIANS...A MODERATE STRENGTH LOW WILL MOVE INTO THE
WESTERN BERING SEA SUNDAY NIGHT AS THE LONGWAVE TROUGH RE-ORGANIZES
FROM THE EASTERN BERING TO THE WESTERN BERING DURING THE SAME TIME
PERIOD. THIS WILL ALLOW THE BENIGN WEATHER CURRENTLY OVER THE WESTERN
BERING TO MOVE EASTWARD...WHILE MORE ACTIVE WEATHER MOVES INTO THE
FAR WESTERN ALEUTIANS ON SUNDAY. A GALE FORCE FRONT WILL MOVE THROUGH
THE ALEUTIANS AND REACH THE ALASKA PENINSULA ON TUESDAY MORNING
BEFORE STALLING AND WEAKENING THROUGH THE END OF THE WEEK.

.LONG TERM FORECAST...
THE EXTREMELY WET PATTERN OVER THE SOUTHERN MAINLAND WILL GRADUALLY
SUBSIDE FOR THE MIDDLE SECTION OF THE WEEK...THOUGH THE LONG-RANGE
MODELS ARE SUGGESTING THE BERING SEA LONGWAVE MAY SHIFT EASTWARD
AGAIN LATE NEXT WEEK. EXPECT CONTINUED CLOUDY CONDITIONS WITH
INCREASING DRYING ACROSS THE MAINLAND AS ACTIVE WEATHER SHIFTS
TEMPORARILY TO THE BERING SEA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...FLOOD ADVISORY 121 131
MARINE...GALE 172 175 176
FIRE WEATHER...NONE

DIXON AUG 13